1. FIELD OF THE INVENTION
This invention relates to an improved process for dyeing unmodified polyolefin articles with aqueous dispersions of solvent dyes and to novel products produced thereby.
2. DESCRIPTION OF THE PRIOR ART
Unmodified polyolefin polymer is very difficult to dye. The polymer is extremely hydrophobic and lacks active groups which could be receptive to dyes. Dye molecules have great difficulty in penetrating the polymer structure. Nonetheless, numerous types of dyes, dye auxiliaries and methods have been suggested for dyeing unmodified polyolefins. Several known processes, such as those disclosed in U.S. Pat. Nos. 3,046,076; 3,069,220 and 3,128,146, involve dissolving a dye in an organic solvent, forming an aqueous dispersion of the solution, applying the dispersion to a polyolefin article and then drying the article. U.S. Pat. No. 3,056,643 discloses vat dyeing of a polypropylene article with an aqueous dispersion of a dye (e.g., an anthraquinone) in the presence of an amine of the formula R--NH.sub.2, wherein R is a hydrocarbon radical having 8 to 22 carbon atoms. Enhancement of the receptivity of a polyolefin article to certain types of dyes by mixing as much as 30% by weight of a fatty acid (e.g., stearic acid) and/or other ingredients into a melt of the polyolefin polymer is disclosed in U.S. Pat. No. 3,231,530 and Japanese Patent Application Publication 15466/62. Though such processes can be useful, improvements still are needed for many commercial applications.
A particularly useful polyolefin article for use as gowns and drapes in hospital operating rooms is made of Tyvek.RTM. spunbonded olefin, a nonwoven sheet manufactured by E. I. du Pont de Nemours and Company from film fibrils of unmodified polyethylene polymer. The sheet desirably combines strong water-barrier characteristics with high air permeability and other satisfactory qualities. However, because the sheet can reflect light excessively, it can cause undesirable glare during some surgical procedures. Accordingly, coloration of the sheet has been necessary. U.S. Pat. No. 4,082,887 suggests providing such nonwoven sheets with coatings that contain pigments and various other ingredients designed to avoid detrimentally affecting the desirable water-barrier and air-permeability characteristics. Though such coatings have been useful, they can be expensive and can have less-than-desirable effects on some sheet characteristics.
It is a purpose of this invention to provide an improved process for dyeing articles, such as fabrics, yarns, fibers, films and the like, especially nonwoven film-fibril sheets, made of unmodified polyolefin polymer.